Adaptive call admission control for use in a wireless communication system

ABSTRACT

The invention relates to communication systems and to systems and methods for implementing adaptive call admission control (CAC) in such systems. Adaptive call admission control can determine what CPE to base station calls (connections) are allowed at any given time. CAC, coupled with precedence, can further determine what connections are suspended if less bandwidth is available than is currently committed. Multiple techniques are disclosed to select connections for suspension. These techniques include suspending enough connections through the affected CPE until there is enough bandwidth to meet the remaining commitment, randomly (or in a round robin fashion) choosing connection to suspend from the entire set of connection, and using precedence priority levels.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/350,464, filed Feb. 8, 2006 now U.S. Pat. No. 7,289,467 which is adivisional of U.S. application Ser. No. 10/032,044, filed Dec. 21, 2001now U.S. Pat. No. 7,023,798, both entitled ADAPTIVE CALL ADMISSIONCONTROL FOR USE IN A WIRELESS COMMUNICATION SYSTEM, which claimspriority to U.S. provisional patent application Ser. No. 60/258,428,filed Dec. 27, 2000, entitled ADAPTIVE CALL ADMISSION CONTROL FOR USE INA COMMUNICATION SYSTEM, all of which are incorporated herewith in theirentirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to communication systems and to a systemand method for implementing adaptive call admission control in suchsystems.

2. Description of the Related Art

A wireless communication system facilitates two-way communicationbetween a plurality of subscriber units (fixed and portable) and a fixednetwork infrastructure. Exemplary communication systems include mobilecellular telephone systems, personal communication systems (“PCS”), andcordless telephones. An objective of these wireless communicationsystems is to provide communication channels on demand between thesubscriber units and their respective base stations in order to connecta subscriber unit end user with the fixed network infrastructure(usually a wire-line system). In the wireless systems having multipleaccess schemes, a time “frame” is used as the basic informationtransmission unit. Each frame is sub-divided into a plurality of timeslots. Subscriber units typically communicate with their respective basestation using a “duplexing” scheme thus allowing for the exchange ofinformation in both directions of the connection.

Transmissions from the base station to the subscriber units are commonlyreferred to as “downlink” transmissions. Transmissions from thesubscriber units to the base station are commonly referred to as“uplink” transmissions. Depending upon the design criteria of a givensystem, wireless communication systems have typically used either timedivision duplexing (“TDD”) or frequency division duplexing (“FDD”)methods to facilitate the exchange of information between the basestation and the subscriber units.

SUMMARY OF THE INVENTION

The systems and methods have several features, no single one of which issolely responsible for its desirable attributes. Without limiting thescope as expressed by the claims which follow, its more prominentfeatures will now be discussed briefly. After considering thisdiscussion, and particularly after reading the section entitled“Detailed Description” one will understand how the features of thesystem and methods provide several advantages over traditionalcommunication systems.

One aspect is a communication system that is configured to control theadmission of new connections and the suspension of existing connectionsbetween a base station and customer premise equipments (CPEs), whereinthe base station and the CPEs are each configured to increase ordecrease the robustness of their transmission modulation technique byadapting their PHY mode. The system comprises a first CPE having a firstmodem configured to modulate data in a communication link using a firstcurrent PHY mode and a first planned PHY mode, a second CPE having asecond modem configured to modulate data in a communication link using asecond current PHY mode and a second planned PHY mode, and a basestation having a third modem configures to transmit and receive data toand from the first and second CPEs. The system further comprises a calladmission control (CAC) module configured to determine whether to allowa new connection between the first CPE and the base station or betweenthe second CPE and the base station based on a comparison of a total airlink line rate between the first and second CPEs and the base station,wherein the total air link line rate is based on a reference PHY mode,with a bandwidth commitment value between the base station and the firstand second CPEs, wherein the bandwidth commitment is based on the firstand second planned PHY modes.

Another aspect is a method for controlling the admission of connectionsin a wireless communication system between a base station and associatedCPEs, including a requesting CPE. The method comprises receiving arequest for a new connection from a requesting CPE, summing the hardbandwidth commitments between a base station and associated CPEs,including the new connection and existing connections, based on aplanned PHY mode for each connection, and determining an air link linerate between the base station and the associated CPEs based on areference PHY mode. The method further includes if the air link linerate exceeds the hard bandwidth commitments, accepting the newconnection and determining a second hard bandwidth commitments for theexisting connections between the base station and the associated CPEsbased on a current PHY mode for each connection, else denying the newconnection. The method still further includes if the air link line rateexceeds the second hard bandwidth commitments, allocating air linkresources to the new connection, else determining whether additional airlink resources are available, and if additional air link resources areavailable, allocating the air link resources to the new connection, elsesuspending at least one of the existing connections between the basestation and the associated CPEs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a wireless communication systemincluding a base station and one or more CPEs.

FIG. 2 is an illustration of the structure of a Time Division Duplex(“TDD”) frame.

FIG. 3 is a block diagram of a modem.

FIG. 4 is a flowchart illustrating the process of adaptively adjusting aPHY mode for an uplink connection between the base station and a CPE.

FIG. 5 is a flowchart illustrating the process of precedence beingapplied to existing connections between the CPE and the base station.

FIG. 6 is a flowchart illustrating the process of call admission controlto a new connection between a CPE and the base station.

DETAILED DESCRIPTION

The following detailed description is directed to certain specificembodiments of the invention. However, the invention can be embodied ina multitude of different systems and methods. In this description,reference is made to the drawings wherein like parts are designated withlike numerals throughout.

In connection with the following description many of the components ofthe various systems, some of which are referred to as a “module,” can beimplemented as software, firmware or a hardware component configured toperform one or more functions or processes. Hardware components caninclude, for example, a Field Programmable Gate Array (FPGA) orApplication-Specific Integrated Circuit (ASIC). Such components ormodules may reside on the addressable storage medium and configured toexecute on one or more processors. Thus, a module may include, by way ofexample, components, such as software components, object-orientedsoftware components, class components and task components, processes,functions, attributes, procedures, subroutines, segments of programcode, drivers, firmware, microcode, circuitry, data, databases, datastructures, tables, arrays, and variables. The functionality providedfor in the components and modules may be combined into fewer componentsand modules or further separated into additional components and modules.Additionally, the components and modules may advantageously beimplemented to execute on one or more computers.

FIG. 1 is a block diagram of an exemplary wireless communication system100. Alternatively, the methods and systems herein disclosed can beimplemented in wired communication systems (not shown). One exemplarybroadband wireless communication system is described in U.S. Pat. No.6,016,311, by Gilbert et al., issued Jan. 18, 2000, entitled “AdaptiveTime Division Duplexing Method and Apparatus for Dynamic BandwidthAllocation within a Wireless Communication System,” hereby incorporatedby reference. The system 100 includes a base station 102 and at leastone customer premise equipment. The system depicted in FIG. 1 showsthree CPEs 104(a)-(c). More or fewer CPEs can be used. The CPEs and thebase station receive and transmit data along wireless communicationlinks 110(a)-(c), 112(a)-(c).

FIG. 1 does not show buildings or other physical obstructions (such astrees or hills, for example), that may cause channel interferencebetween data from communication links 110, 112. The CPEs 104 and thebase station 102 communicate by transmitting their data as radiofrequency signals. The term channel refers to a band or range of radiofrequencies of sufficient width for communication. For example, therange of frequencies from 26.500 GHz to 26.525 GHz would provide a 25MHz wide channel. Although the following discussion uses the example ofa system that transmits information within the Local Multi-PointDistribution Services (LMDS) band at frequencies of approximately 28GHz, the invention is not so limited. Information can be transmitted atvarious frequencies and ranges including, for example, 10 GHz to 66 GHzusing Quadrature Amplitude Modulation (QAM) symbols. The systems andmethods described herein can also be used in a Multichannel Multi-pointDistribution Service (MMDS) which operates below 10 GHz. In the MMDS,Orthogonal Frequency Division Multiplexing (OFDM) symbols may betransmitted between the base station and CPEs as an alternative tosingle carrier QAM modulation. In such a system, the methods and systemsare applied to one or more of the OFDM subchannels.

Referring again to FIG. 1, the communication links 110(a), 110(b),110(c) are referred to as downlinks (i.e., from the base station 102 tothe CPE's 104) and can operate on a point (base station)-to-multi-point(CPE's) basis. Transmissions to and from the base station 102 can bedirectional in nature, and thus limited to a particular transmissionsector 106 of the base station 102. Within a given sector 106, CPEs104(a), 104(b), 104(c) receive the same transmission along theirrespective downlinks 110(a), 110(b), 110(c). To distinguish between dataintended for a specific CPE, the CPEs can monitor control information intheir respective downlink 110(a), 110(b), 110(c) and typically retainonly the data intended for them. In communication systems that havemultiple sectors, the base station 102 can include a sectored activeantenna array (not shown) which is capable of simultaneouslytransmitting to multiple sectors. In one embodiment of the system 100,the active antenna array transmits to four independent sectors.

The communication links 112(a), 112(b), 112(c) are referred to as anuplink (i.e., from the CPEs 104 to the base station 102) and can operateon a point-to-point basis. Thus, in FIG. 1, each CPE 104(a), 104(b),104(c) originates its own uplink 112(a), 112(b), 112(c). Communicationwith the base station 102 is bi-directional and can be multiplexed onthe basis of Time Division Duplexing (TDD). For a TDD transmission from,for example, CPE 104(a), CPE 104(a) would send its data alongcommunication link 112(a) to the base station 102 during a preassignedtime slot in a transmission frame. The specific frame structures of theuplink and downlink will be discussed further below.

Alternatively, the system can employ Frequency Division Duplexing (FDD).In such an FDD system, duplexing of transmissions between the basestation and the CPEs is performed in the frequency domain. Differentsets of frequencies are allocated for uplink and downlink transmissions.The systems and methods described herein can be used in such an FDDsystem.

Each CPE 104 is further coupled to a plurality of end users that mayinclude both residential and business customers. Each customer can haveone or more connections between the CPE and the base station.Consequently, each end user connection can have different and varyingusage and bandwidth requirements. Each CPE 104(a)-(c) may serviceseveral hundred or more end users, but at least one end user will beassigned to transmit and receive data via at least one connectionthrough each CPE 104.

The data transmitted along the communication links 110, 112 is in analogform, and thus a modem 108 is used to modulate the digital data prior totransmission. FIG. 1 illustrates the modem 108 being located at the basestation 102, however, a similar or identical modem 108 may be used atthe other end of the downlinks 110(a), 110(b), 110(c) to demodulate thereceived analog data. Thus, the modems 108 in the base station and eachCPE are used for uplinking data from the CPEs to the base station andfor downlinking data from the base station to the CPEs.

The base station and CPEs can use adaptive modulation and forward errorcorrection (FEC) schemes to communicate. Adaptive modulation, oradaptable modulation density, includes varying the bit per symbol ratemodulation scheme, or modulation robustness, of downlinks and uplinkstransmitted between CPEs and the base station. Examples of suchmodulation schemes include quadrature amplitude modulation-4 (QAM-4),QAM-16, QAM-64, and QAM-256. If QAM-4 is used, each resulting symbolrepresents two bits. If QAM-64 is used, each resulting symbol representssix bits. Adaptive FEC includes varying the amount of error correctiondata that is transmitted in the downlink and/or uplink. Channelcharacteristics, for example the modulation and FEC, for the downlinkand/or uplink can be varied independently. For ease of explanation, thephrase “PHY mode” is used to indicate characteristics of a communicationchannel or link, including for example, modulation scheme and/or an FEC.

The PHY mode(s) planned for use in the sector 106 is normally determinedas a function of the geographical relationship between the base station102 and the CPEs, the rain region, and the implementation or modemcomplexity of the CPEs. Examples of rain regions include rain regionsA-Q. Recommendations for modeling the rain region's effect on signalpropagation can be found in Rec. ITU-R PN.837.1. Thus, a planned PHYmode may be different for the CPEs depending on the capabilities andtransmission quality of each CPE 104 and base station 102 pair. For easeof explanation, the phrase “planned PHY mode” is used to indicate theplanned PHY mode for a CPE 104 and base station 102 pair as describedabove.

Better environmental conditions, e.g., less distance, between some CPEs(such as CPE 104(c) for example) and the base station 102 may permit theuse of a less robust PHY mode by such CPEs as compared to a PHY modeused by CPEs located farther from the base station. For example, if CPE104(c) is capable of receiving QAM-64 data coupled with achievingadequate transmission quality between CPE 104(c) and the base station102, all data transmitted between the CPE and the base station can bemodulated using QAM-64. In the same system CPEs 104(a), 104(b), which,for example, are only capable of receiving QAM-4 data, will onlytransmit and receive QAM-4 data. By using different or variable PHYmodes for different CPEs associated with a single base station, thecommunication system 100 as a whole increases its bandwidth utilization.

The transmission quality between the base station 102 and a CPE 104 maynot only vary between each CPE and base station pair as described above,but may also vary over time, or between the uplink and downlinktransmissions of a single pair (i.e. asymmetrical transmissions). Forexample, in FIG. 1, the transmission quality may significantly decreaseduring a rain or snow storm. When the link quality is decreased, thereis an increased chance that transmitted data along communication links110(a), 110(b), 110(c), 112(a), 112(b), 112(c) may be unrecognizable orlost to the receiving base station or CPE. To accommodate these timevariations in link quality, the communication system 100 can dynamicallyadjust or “adapt” the PHY mode for each base station 102 and CPE 104. Insuch an adaptive system, the bandwidth utilization of the communicationsystem 100 further increases.

FIG. 2 represents a time division duplexing (“TDD”) frame andmulti-frame structure for use in communication system 100. Frame 300includes a downlink subframe 302 and an uplink subframe 304. Thedownlink subframe 302 is used by the base station 102 to transmitinformation to the CPEs 104(a)-(c). In any given downlink subframe 302,all, some, or none of the transmitted information is intended for aspecific CPE 104. The base station 102 may transmit the downlinksubframe 302 prior to receiving the uplink subframe 304. The uplinksubframe 304 is used by the CPEs 104(a)-(c) to transmit information tothe base station 102.

Subframes 302, 304 are subdivided into a plurality of physical layerslots (PS) 306. Each PS 306 correlates with a duration of time. In FIG.2, each subframe 302, 304 can be one-half millisecond in duration andinclude 400 PS for a total of 800 PS per frame 300. Alternatively,subframes having longer or shorter durations and with more or fewer PSscan be used. Additionally, the size of the subframes can be asymmetricaland can be varied over time.

Each downlink subframe 302 can include a frame control header 308 anddownlink data 310. The frame control header 308 includes information forthe CPEs to synchronize with the base station 102. The frame controlheader 308 can include control information indicating where a PHY modechange occurs in the downlink. The frame control header 308 can alsoinclude a map of a subsequent uplink subframe 304. This map allocatesthe PSs 306 in the uplink subframe 304 between the different CPEs. Theframe control header 308 can further include a map of attributes of thedownlink data 310. For example, attributes may include, but are notlimited to, the locations of the PSs 306 in the subframe 302 that areintended for each individual CPE.

The downlink data 310 is transmitted using a pre-defined PHY mode or asequence of PHY modes with three PHY modes A, B, and C depicted in FIG.2 as an example. Individual or groups of PSs 306 in the downlinksubframe 302 are assigned to data intended for specific CPEs 104. Forexample, the base station 102 could assign PSs in one, some, or all ofthe PHY modes A, B, and C for transmitting data to CPE 104(a). In FIG.2, the data is divided into three PHY modes, where PHY mode A (312(a))is the most robust modulation (i.e. least prone to transmission errorscaused by signal interference) and while PHY mode C (312(c)) is theleast robust (i.e. most prone to transmission errors caused by signalinterference). In between these PHY modes is PHY mode B (312(b)).Additional PHY modes can also be used.

Still referring to FIG. 2, the uplink subframe 304 comprises uplink data314(a)-(n). The uplink subframe 304 is used by the CPEs 104(a)-(c) totransmit information to the base station 102. The subframe 304 issubdivided into a plurality of PSs 306. Each CPE 104(a)-(c) transmitsits information during its allocated PS 306 or range of PSs 306. The PSs306 allocated for each CPE can be grouped into a contiguous block of aplurality of data blocks 314(a)-(n). The CPEs use data blocks 314(a)-(n)to transmit the uplink subframe 304. The range of PSs 306 allocated toeach block in the plurality of data blocks 314(a)-(n) can be selected bythe base station 102. The data transmitted in each data block 314(a)-(n)is modulated by the transmitting CPE. For example, CPE 104(a) modulatesand transmits uplink data block 314(a). The same or different PHY modescan be used for each data block 314(a)-(n). The data blocks 314(a)-(n)can also be grouped by PHY mode.

During its data block, the CPE transmits with a PHY mode that isselected based on measured channel parameters from its priortransmission(s). Similarly, the base station can select a downlink PHYmode for a communication link based on measured channel parameters fromits prior transmission(s). The process for selecting a PHY mode will beexplained in more detail below. The measured channel parameters can beincluded in the uplink subframe 304 for transmission by the CPEs to thebase station or can be included in the downlink subframe 302 fortransmission by the base station to the CPE. Once received, the basestation or CPE can utilize the channel parameters to determine if thePHY mode of the downlink subframe 302 or the uplink subframe 304 shouldbe changed.

Each CPE 104 can receive all downlink transmissions that are modulatedusing its current PHY mode or are modulated using a more robust PHY modethan its current PHY mode. The frame control header 308 is typicallymodulated using the most robust PHY mode to ensure that all CPEs104(a)-(c) may receive it. Because each CPE receives the frame controlheader, each CPE 104 is initially synchronized with the downlinksubframe 302 at the beginning of the frame 300. The downlink subframecan be sorted by robustness, which allows each CPE to maintainsynchronization during the subsequent portion of the downlink that couldinclude data for that CPE.

FIG. 3 is a block diagram of a modem 108 which can be used tomodulate/demodulate data in the wireless communication system 100described above. The modem 108 is used to control the number and qualityof existing and new connections between the CPEs and base station.Modems 108 are used by the base station 102 and CPEs 104 to modulate anddemodulate data. For ease of description, the modem 108 will now bedescribed with reference to the base station 102.

The modem 108 can include a control section 108(a) and a modem section108(b). The modem section 108(b) includes a receiver module 202 and atransmitter module 204. The control section 108(a) includes a calladmission control (CAC) module 206, a Receive Signal Quality (RSQ)module 208, a precedence module 210, and a control module 212.Alternatively, the functionality provided for by the control section108(a) can be separate from the modem 108. Further, the control section108(a) components and modules may be combined into fewer components andmodules or further separated into additional components and moduleswithin the base station 102 and/or CPE 104.

At a base station 102, the transmitter module 204 converts digital datato an appropriately modulated analog signal communicated as a downlink110, using for example, QAM modulation and FEC. The analog signal mayalso be up converted to a carrier frequency prior to transmission. Thereceiver module 202 at the base station 102 demodulates an uplink112(a), 112(b), 112(c) and converts it back to digital form. Whenconfigured as a CPE 104(a), the transmitter module 204 converts digitaldata to an appropriately modulated analog signal communicated as anuplink 112, using for example, QAM modulation and FEC. The analog signalmay also be up converted to a carrier frequency prior to transmission.The receiver module 202 at the CPE 104 demodulates a downlink 110 andconverts it back to digital form.

The wireless communication system 100 can provide “bandwidth-on-demand”to the CPEs. Thus, the uplink can include bandwidth requests for new andexisting connections from end users. The CPEs request bandwidthallocations from their respective base station 102 based upon the typeand quality of service requested by the end users served by the CPE. ACPE or base station can continue an existing connection or allow a newconnection depending on, for example, a user's defined quality ofservice, bandwidth needs, and transmission quality. Thus, each end userpotentially uses a different broadband service having differentbandwidth and latency requirements. Moreover, each user can select aportion(s) of their bandwidth to have variable priority levels, orprecedence.

To this end, the type and quality of service available to the end usersare variable and selectable. The amount of bandwidth dedicated to agiven service can be determined by the information rate and the qualityof service required by that service (and also taking into accountbandwidth availability and other system parameters as will be describedbelow). For example, T1-type continuous data services typically requirea great deal of bandwidth having well controlled delivery latency. Untilterminated, these services require constant bandwidth allocation foreach downlink subframe 302 and uplink subframe 304 in a frame 300 (seeFIG. 2). In contrast, certain types of data services such as InternetProtocol data services (“TCP/IP”) are bursty, often idle (which at anyone instant may require zero bandwidth), and are relatively insensitiveto delay variations when active.

Referring again to FIG. 3, the Receive Signal Quality (RSQ) module 208interfaces with the receiver module 202 and the control module 212. TheRSQ module 208 is configured to monitor signal quality of the receiveduplink signal. In a communication system that adapts PHY modes, theselection of a PHY mode can be based on channel parametersmonitored/measured by the RSQ module 208. These channel parameters caninclude the signal to noise ratio (SNR) of the modulated data at thereceive module 202 at the base station 102. A bit error rate (BER), atthe base station 102 or CPE 104, can also be used in selecting the PHYmode. For example, when the received signal drops below a thresholdvalue for a SNR, a more robust PHY mode can be selected by the modem 108for the connection. Signal quality can be measured over a period of timeby the RSQ module 208, and, in response to changes in the signalquality, the control module 212 determines if the PHY mode for thetransmitting CPE should be changed. The control module 212 at the basestation 102 interfaces with the transmitter module 204 to control thePHY mode for the modem 108. Further, the control module 212, via thetransmitter module 204, can alert the transmitting CPE to change its PHYmode. Measuring signal quality over time helps avoid cyclic changes inthe PHY mode due to transient changes in the communication link'squality.

The RSQ module at the CPE can measure signal quality for a signal thatis transmitted by the base station 102 and received by the CPE. The CPEcan alert the base station to change the base station's transmitting PHYmode. In one embodiment, only the modem 108 at the base station 102includes the control module 212. In this embodiment, each CPE measuresits own signal quality and transmits its value within its uplink 112 tothe base station 102. The control module 212 is then able to monitor thesignal quality of the signal received by the CPEs to determine if thedownlink 110 PHY modes should be changed.

The call admission control (CAC) module 206 determines what CPE to basestation connections are allowed at any given time. For example, thereceiver module 202 can receive a request for a new connection betweenthe CPE and base station in the uplink 112. The CAC module determineswhether to grant that request. This determination can be based onintrinsic factors relating to the new connection as well ascommunication system level factors. Examples of intrinsic factors are aquality of service and a type of service requested by the end user forthe new connection. The extrinsic factors are external to the newconnection. The extrinsic factors can include the type and quality ofservice for the existing connections, whether available bandwidth isallocated to the requesting CPE, the available bandwidth in thecommunication link, and the portion of the frame that is allocated forthe uplink and downlink. An example of a type and quality of servicethat can be evaluated by the CAC module 206 are hard bandwidthcommitments.

The CAC module 206 can be configured to determine whether there will beenough bandwidth to support all of the connections between the CPEs 104and the base station 102. For example, the CAC module 206 can determinewhether there will be enough bandwidth for hard bandwidth commitmentsbetween the base station and CPEs. These hard bandwidth commitments caninclude, for example, constant bit rate (CBR) connections, the minimumcell rate (MCR) portion of a guaranteed frame rate (GFR) connections,and some function of sustainable cell rate (SCR) for variable bit rate(VBR) and variable bit rate real-time (VBR-rt) connections.Alternatively, hard bandwidth commitments could be the bandwidthmeasured, rather than calculated, that is necessary to provide thequality of service (QoS) desired for the connection. For ease ofexplanation, the following description uses hard bandwidth commitmentsas an exemplary type of connection. However, the systems and methodsdisclosed herein are not so limited and can be applied to any type ofconnection. Further, the systems and methods can be applied to one ormore types of connections.

The CAC module 206 determines whether there is enough bandwidth to allowthe new connection. This can be determined by summing the hard bandwidthcommitments for each connection on each CPE 104(a), 104(b), 104(c) (seeFIG. 1). Thus, each CPE will have a hard bandwidth commitment for itsexisting connections. All of the hard bandwidth commitments from theCPEs can then be summed to get the total hard bandwidth commitments forall of the existing connections through base station 102. The controlmodule 212 can perform these calculations. The CAC module 206 comparesthe total hard bandwidth commitments to an air link line rate. The airlink line rate is the amount of bandwidth available between the CPEs andbase station. If the air link line rate exceeds the total hard bandwidthcommitments, the new connection is allowed. If the total hard bandwidthcommitments meet or exceed the air link line rate, the CAC module 206denies the new connection.

In the communication system described above, each connection between theCPE 104 and base station 102 will have a planned PHY mode. The plannedPHY mode is used by the CAC module 206 in determining whether to allowthe new connection. As will be explained below, the calculation of thetotal hard bandwidth commitments for any given sector 106 (see FIG. 1)presents additional difficulties for communication systems 100 whichadapt PHY modes.

In communication systems 100 that adapt, or vary, their PHY modes, theavailable bandwidth necessary for existing connections can vary. Sinceeach PHY mode used by the base station 102 and/or CPE 104 for itscommunication link 110(a)-(c), 112(a)-(c) is adaptive, the robustness ofeach communication link can vary (see FIG. 1). As the robustness varies,the bandwidth allocated for an existing connection or new connectionwill also vary.

In such communication systems, connections are allowed to be modulatedwith PHY modes that are more or less robust than the planned PHY mode.Each end user connection can dynamically select its current PHY mode.This current PHY mode can be different than the planned PHY mode thatwas planned for the connection. If a connection is modulated using amore robust PHY mode than the planned PHY mode, the connection willexceed its allocated bandwidth.

In an embodiment of a communication system 100 that adapts PHY modes,the CAC module 206 allows new connections with reference to a minimumair link line rate. The minimum air link line rate is a measure ofbandwidth that would be required if all of the existing connectionsbetween the CPEs and base station were modulated using a least efficientPHY mode regardless of whether the least efficient PHY mode is actuallyused. The least efficient PHY mode can include, for example, QAM-4modulation with a maximum amount of FEC overhead bits. This methodensures that during adverse weather conditions each CPE will be able toselect its least efficient PHY mode and transmit its data within itsassigned bandwidth without losing its connection with the base station.In this embodiment, the CAC module 206 will deny a new connection if thenew connection will cause the CPE to exceed its minimum air link linerate. The CAC module 206 can determine whether to allow or deny a newconnection in conjunction with the control module 212. During spells ofgood weather, the CPE can select a less robust PHY mode for its currentPHY mode. By selecting a less robust PHY mode, additional bandwidthbetween the CPE and base station would be freed up. However, thecommunication system 100 is constrained from taking advantage of thefreed up bandwidth when the decision to allow new connections is basedupon the minimum air link line rate.

In another embodiment of the communication system 100 that adapts PHYmodes, the CAC module 206 allows the CPE to take advantage of the freedup bandwidth. The CAC module 206 limits new connections based on acomparison of the bandwidth required for the connection if it ismodulated using the CPE's planned PHY mode with the available bandwidth.The available bandwidth is determined by summing the CPE's hardbandwidth commitments that would be used by the existing connections ifthose connections were modulated using the planned PHY mode of the CPE.If the available bandwidth is equal to or exceeds the bandwidth requiredfor the new connection, the CAC module 206 will allow the connection.However, if the CPE operates using a less robust PHY mode than itspreferred PHY mode, there is the potential that data through the CPEwill be lost.

In the presence of adaptive PHY modes and to take advantage of the CPE'splanned PHY mode, the bit rate associated with each connection's PHYmode is compared. Connections at different PHY modes (modulation andFEC) effectively have different bit rates, or air link line rates, andthus are not directly compared. One method for comparing these bit ratesis to normalize the PHY modes associated with each connection.

Equation 1, below, can be used to normalize the bandwidth used forconnections through an individual CPE.

$\begin{matrix}{W_{CPEi} = {\sum\limits_{i = 1}^{n}{{ER}*{mod}}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

Where W_(CPEi) is a normalized value or weight for the entire bandwidthused by an individual CPE. W_(CPEi) is proportional to the equivalentbandwidth of its connections and the current modulation associated witheach connection. Er is the number of bits per unit time that aretransmitted by the CPE for a connection. Each connection is modulatedusing an associated PHY mode. The term mod is the inverse of theassociated PHY mode efficiency that is used to modulate the connection.The bit/symbol rate for QAM-64 is 6, for QAM-16 is 4, and for QAM-4 is2. For example, if during a first connection between CPE 104(a) and thebase station 102, 10,000 bits/s were transmitted using QAM-4, and duringa second connection between CPE 104(a) and the base station, 18,000bits/s were transmitted using QAM-64, Equation 1 would be:W _(CPE104(a))=(10,000 bits/s* 1/2 symbol/bit)+(18,000 bits/ s* 1/6symbol/bit)=8,000 bits/s.

The 8,000 bits/s for CPE 104(a) is then added to W_(CPE104(b)) andW_(CPE104(c)) to determine a total normalized bandwidth for the CPEs insector 106.

Normalization is used to determine the effective hard bandwidthcommitment usage through the modem 108. The CAC module 206 interfaceswith the control module 212 to compare the different PHY modes for theexisting connections and the new connection with the available bandwidthbetween the base station 102 and CPEs 104. In this embodiment, thecontrol module 212 is configured to normalize each CPE's air link linerate. Once the control module 212 has determined the normalized valuefor each CPE's committed bandwidth requirements, the CAC module 206 cansum and compare them against a common air link line rate.

Equation 2, below, can be used by the CAC module 206 to determine thetotal bandwidth used, i.e. W_(Link)−W, by all of the CPEs in the sector.

$\begin{matrix}{W_{Link} = {\sum\limits_{i = 1}^{n}W_{CPEi}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

Where W_(CPEi) is a normalized value or weight for the entire bandwidthused by an individual CPE in the sector.

For example, with PHY modes of QAM-4, QAM-16, and QAM-64, each using thesame FEC, QAM-4 requires 3 times the air link resources, or bandwidth,of QAM-64 and QAM-16 requires 1.5 times the air link resources ofQAM-64. In this example, the control module 212 can normalize to QAM-64.Thus, CPEs operating at QAM-64 would have their hard bandwidthcommitments multiplied by a weight of 1, CPE's operating at QAM-16 wouldhave their hard bandwidth commitments multiplied by a weight of 1.5, andCPE's operating at QAM-4 would have their hard bandwidth commitmentsmultiplied by a weight of 3. The CAC module 206 then sums these hardbandwidth commitments and compares the total against a line rate of acommunication link operating entirely at the selected normalized PHYmode, QAM-64 with the single FEC. Alternatively, the control module 212normalizes to QAM-4 by applying weights of ⅓ to QAM-64, 1/2 to QAM-16,and 1 to QAM-4. The selection of QAM-64 and QAM-4, each with a singleFEC, for use as a normalization PHY mode are only examples. Any PHY modecould be used to define the air link line rate for normalizing theconnections between the CPEs and base station.

Still referring to FIG. 3, the precedence module 10 will now bedescribed. The precedence module 210 interfaces with the receiver module202 and the control module 212 to apply a priority, or precedence, toone or more connections when less bandwidth is available than requiredto meet the hard bandwidth commitments. This can occur when the CACmodule 206 is configured as described above to limit new connectionsbased on planned PHY modes of the CPEs but some or all of the CPEs areoperating at a more robust (less efficient) current PHY mode. Theprecedence module 210 determines which connection(s) are to besuspended. However, before connections are suspended, the base station102 can re-allocate bandwidth, that is not intended for hard bandwidthcommitments, among the CPEs to increase the available bandwidth for hardbandwidth commitments. Alternatively or in addition to, in TDD systems,the base station 102 can adjust the portion of a downlink subframe 302and of an uplink subframe 304 in the frame 300 (see FIG. 2) to increasethe available bandwidth for a CPE that requires additional bandwidth dueto a change in the current PHY mode or the addition of a connection.However, if additional bandwidth is not available, the precedence module210 selects which connections from among the CPEs are suspended.

Bandwidth problems can arise when one or more CPEs are using more robustPHY modes than their planned PHY modes for their connections. Forexample, if communication system 100 was designed for 99.99%availability, a comparison would be made between a CPE's geographicalproximity to the base station and the communication system's rainregion. Based on this comparison, a planned PHY mode is selected forthat CPE that allows it to operate at that planned PHY mode or a lessrobust PHY mode the entire year except for approximately 53 minutes. Ifa CPE exceeds a SNR or BER threshold and transmits its uplink using amore robust PHY mode than its planned PHY mode, it will requireadditional bandwidth for these 53 minutes. At least two things can occurduring this 53 minutes depending on whether additional air linkresources in the communication system 100 are available. Shouldadditional bandwidth be needed when only a few existing connections,between the base station 102 and CPEs 104 in sector 106, select amorerobust PHY mode, the base station 102 may be able to reallocate theavailable bandwidth. Thus, if the communication system is sufficientlyunder subscribed, the CPE 104 can use the additional air link resourcesit requires when using a more robust PHY mode than its planned PHY modeduring the 53 minutes. If many existing connections between the basestation and CPEs are subject to similar adverse environmentalconditions, the base station 102 may be unable to accommodate the CPEs'bandwidth requests. When the air link resources aren't available, theprecedence module 210 selects which of the existing connections from theCPEs 104 (a)-(c) to suspend.

The precedence module 210 interfaces with the control module 212 tocompare the bit rates for the existing connections through each CPEbased on each CPE's current PHY mode. While the CAC module 206 comparesthe planned PHY modes of the CPEs to determine whether a new connectionis allowed, the precedence module 210 compares the current PHY modes tothe selected reference air link line rate to determine if a suspensionshould occur. The control module 212 is configured to compare thecurrent PHY modes of the CPEs. As explained above, one method forcomparing the PHY modes is normalization. Once normalized, theprecedence module 210 determines if additional bandwidth between theCPEs and base station is available. If additional bandwidth isavailable, the precedence module 210 can determine a margin value. Ifadditional bandwidth is not available, the precedence module 210 selectswhich connections are going to be suspended.

The precedence module 210 can be configured to suspend enoughconnections through the CPE that is requesting additional bandwidthuntil there is enough bandwidth to meet the remaining demand. The amountof outage during the year for the connections through the affected CPE104 is planned based on the availability and rain region as discussedabove. CPEs 104 located at greater distances from the base station 102or having limited visibility of the base station would more likely besubject to the application of precedence. In this embodiment, CPE's arepenalized by their geographic proximity to the base station 102. Forexample, the same CPEs, those that are barely able to meet theiravailability numbers at their planned PHY modes, would be the first tohave their hard bandwidth connections with the base station 102suspended. These CPEs may receive the full brunt of the planned 53minutes per year outage. In contrast, other CPEs (in particular, thosebarely unable to meet the availability number at the next less robustPHY mode) would have plenty of bandwidth because connections through thegeographically challenged CPE's would be suspended before they need todrop to a more robust PHY mode and request additional bandwidth.

Alternatively, the precedence module 210 can also randomly selectconnections for suspension or select them in a round robin fashion. Theprecedence module 210 chooses connection to suspend from the entire setof connections that have hard bandwidth commitments through the CPEs inthe sector 106. The CPEs subject to potential suspension include CPEsthat may still be operating at their planned PHY mode. In thisembodiment, the communication system 100 as a whole, and each individualconnection still meets its availability numbers since the planned outageis evenly shared. For example, if a rain fade caused the base station102 and CPEs to lose half of their bandwidth, each connection from amongall of the CPEs would, on average, see only 26 minutes outage per yearrather than 53 minutes. Thus, the precedence aspect of adaptive CAC canallow you to increase system availability (26 minutes outage vs 53minutes outage) or capacity. For example, operating a CPE 104 at a lessrobust PHY mode than would typically be planned for the CPE increasesthe system's capacity. The communication system can rely on adaptive CACcoupled with precedence to distribute the outage among all of the CPEs.This achieves the planned 53 minutes outage, but with increasedmodulation efficiency for the CPE operating at the less robust PHY mode.

Further, the precedence module 210 can use levels in conjunction withthe random selection method discussed above when selecting whichconnections to suspend. In this embodiment, each connection between theCPEs 104(a)-(c) and base station 102 is assigned a precedence level.Alternatively, each CPE is assigned a precedence level for itsconnections. For example, there are five levels, one through five, withprecedence level one being assigned to the most important connectionsand precedence level five being assigned to the least importantconnections. The random selection of connections for suspension isapplied as discussed above with reference to the second embodiment.However, instead of applying the method of the second embodiment to allconnections simultaneously, the precedence module 210 applies it basedon each connection's assigned precedence level. Continuing with theexample above, the random selection would be initially applied toconnections assigned to precedence level five. If and when theprecedence level five connections are exhausted, the precedence module210 applies the random selection process to connections assigned toprecedence level four and so on until there is adequate bandwidthavailable for the remaining connections that have hard bandwidthcommitments. Thus, individual connections can be selected to have theiruplink or downlink transmissions suspended in favor of otherconnections.

Further, the precedence module 210 can allow connections to continue tooperate with their current PHY mode even when a first SNR or BERthreshold is exceeded. Instead, a second threshold is implemented tomaintain the connection at the same PHY mode. However, the error rateassociated with the connection may increase.

FIG. 4 is a flowchart illustrating the process of adaptively adjusting aPHY mode for a connection between the base station 102 and a CPE. Thisprocess can be implemented by a modem 108 at a base station.Alternatively, this process is performed by a modem 108 at the CPE. Aspecific CPE 104 can change its uplink PHY mode independent of thatCPE's downlink PHY mode. The specific CPE's PHY mode can also beindependent of the uplink PHY modes used by other CPEs 104 within thesame sector 106. Because the base station 102 must synchronize with eachindividual CPE 104 that uplinks data, the uplink quality may bedifferent than the downlink quality with a specific CPE 104. The basestation 102 can perform the process of adaptively adjusting the uplinkPHY mode used by a specific CPE 104. As such, a similar process may becompleted for each CPE 104 within the sector 106 in order to adaptivelyadjust each CPEs 104 uplink modulation.

The following description describes a process for adaptively adjusting aPHY mode for an uplink from a CPE to a base station. The same process isused for adaptively adjusting a PHY mode for a downlink from the basestation to the CPE.

In particular, flow begins in start block 400. Flow moves to a block 402where a receiver module 202 at a base station 102 receives an uplinkfrom a CPE 104. Flow proceeds to block 404, where the quality of thechannel parameters for the uplink 112 is determined by a receive signalquality (RSQ) module 208. The quality may be a function of the state ofthe transmission medium (e.g. air, foggy air, wet air, smoky air, etc.)and the ability of both the transmitting and receiving components (e.g.CPE 104 and base station 102) to respectively transmit and receive data.The base station 102 can determine the quality of each uplink112(a)-(c). Alternatively, the base station 102 periodically transmitschannel parameter measurements, which are indicative of the quality of aCPE's uplink 112, to that CPE 104. The CPE 104 then uses these channelparameter measurements to determine the quality of its uplink. Thesechannel parameter measurements can include a SNR and/or a BERmeasurement of the uplink 112(a)-(c). For example, base station 102 candetermine the quality of uplink 112(c) based on a measurement by its RSQmodule 208 (see FIG. 3). A single SNR measurement or a series of severalSNR measurements taken during a frame 300 (see FIG. 2) or duringmultiple frames may be used to determine the uplink quality. The controlmodule 212 can analyze multiple measurements to determine an uplink'squality.

Continuing to block 406, the base station 102 or CPE 104 compares thecalculated uplink quality with a current PHY mode threshold. The currentPHY mode threshold can include an upper threshold and a lower thresholdat which the PHY mode is changed. For example, if CPE 104(a) iscurrently uplinking data to base station 102 using PHY mode B, the PHYmode will change when the uplink quality exceeds an upper threshold orgoes below a lower threshold.

Next at decision block 408, the CPE determines whether the uplinkquality has decreased and crossed a PHY mode lower threshold accordingto the comparison made in block 406. Continuing with the example above,if the PHY mode lower threshold associated with PHY mode B has not beencrossed, flow proceeds to decision block 410 where the system determineswhether the uplink quality has crossed an upper PHY mode thresholdassociated with PHY mode B. If the current modulation upper thresholdhas been exceeded, flow continues to block 412 where the PHY mode ischanged to a less robust, denser modulation. For example, PHY mode C isselected for CPE 104(a). The base station 102 can send a request to theCPE 104 indicating a desired uplink PHY mode change. Alternatively, thebase station 102 transmits an uplink map to all CPEs 104 in the downlinksubframe 302 (see FIG. 2) indicating which CPEs have been allotteduplink PS's and the PS's associated PHY modes. The base station 102indicates to an individual CPE 104 that the PHY mode has been changed byallotting uplink subframe 304 PSs to that CPE that use a less robust PHYmode. For example, if the uplink PHY mode for CPE 104(a) is to bechanged from PHY mode B to PHY mode C, the base station 102 assignsuplink subframe PS's which are to be modulated using PHY mode C. Thisuplink assignment serves as an indicator to the CPE that its uplink PHYmode has been change. Flow continues to a block 413 where the system canreallocate the newly available bandwidth. For example, the newlyavailable bandwidth can be allocated for new or existing hard bandwidthcommitments, new connections, or connections that had been previouslysuspended. Flow then returns to block 402 as described above.

Returning to decision block 410, if the current PHY mode upper thresholdhas not been exceeded, flow continues to block 402 as described above.

Returning to decision block 408, if the PHY mode lower threshold hasbeen crossed, flow proceeds to a decision block 414 where the systemdetermines whether the connections, between the CPE and base stationthat have a hard bandwidth commitment, are using a less robust PHY modethan the planned PHY mode for the connections. If the connection(s) isusing a less robust PHY mode than its planned PHY mode, the processproceeds to block 416 where a more robust PHY mode is selected for theconnection(s). If the base station determines whether the uplink qualityhas crossed a threshold, the base station 102 can send a request to theCPE 104 indicating a desired uplink PHY mode change. Alternatively, thebase station 102 can transmit an uplink map to all CPEs 104 in thedownlink subframe 302 indicating which CPEs have been allotted uplinkPS's along with the PS's associated PHY modes. This allows the basestation 102 to indicate to an individual CPE 104 that the PHY mode hasbeen changed by allotting uplink subframe 304 PSs to that CPE that usesa more robust PHY mode. For example, if the uplink PHY mode for CPE104(a) is to be changed from PHY mode B to PHY mode A, the base station102 assigns uplink subframe PS's which are to be modulated using PHYmode A. This uplink assignment serves as an indicator to CPE 104(a) thatits uplink PHY mode has been change. Flow then continues to block 420where a precedence module 210 (see FIG. 3) determines whetherconnections between the base station and the CPEs are to be suspended.Precedence will be explained with reference to FIG. 5. Flow thencontinues to block 402 as described above.

Returning to decision block 414, if the connection's current PHY mode isat least as robust as its planned PHY mode, the process continues todecision block 418 where the control module 212 can replace the lowerthreshold associated with the current PHY mode of the connection thathas the hard bandwidth commitment with a second lower threshold. Theprocess continues to block 402 as described above except that at block406 the RSQ module 208 and the control module 212 use the second lowerthreshold to compare with the measured signal quality of the connection.

Returning to decision block 418, if the control module d es not selectthe second lower threshold, the process moves to a block 420, asdescribed above, where the precedence module 210 (see FIG. 3) determineswhether connections between the base station and the CPEs are to besuspended. Precedence will be explained with reference to FIG. 5. Onceprecedence has been applied, the process returns to state 402 asdescribed above.

FIG. 5 is a flowchart illustrating the process of applying precedence toexisting connections between the CPEs 104 and the base station that havehard bandwidth commitments. This process can be implemented by a modem108 at a base station. Alternatively, this process is performed by amodem 108 at the CPE. Flow begins in start block 600. Flow moves toblock 601 where a more robust PHY mode is selected for the existingconnection. Flow proceeds to block 602 where the control module 212determines an air link line rate based on a reference PHY mode. Flowmoves to block 603 where the control module calculates the hardbandwidth commitments for the existing connections between the basestation 102 and CPEs 104 based on the current PHY mode for eachconnection. Flow moves to a decision block 604 where the precedencemodule 210 determines whether the air link line rate determined at block602 exceeds the hard bandwidth commitments between the CPEs and basestation. If the air link line rate exceeds the hard bandwidthcommitments, the process continues to a block 606 where the more robustPHY mode selected in block 601 is applied for the existing connection.Flow then returns to block 402 of FIG. 4 where the base station 102receives the next uplink from a CPE 104.

Returning to decision block 604, if the air link line rate does notexceed the hard bandwidth commitments, flow proceeds to a decision block608 where the precedence module 210 determines whether additional airlink resources are available. These additional air link resources caninclude available bandwidth in the uplink subframe 302 and availablebandwidth in the downlink subframe 304 (see FIG. 2). If additional airlink resources are available, flow proceeds to block 606 where the morerobust PHY mode is applied for the existing connection. Flow thenreturns to block 402 of FIG. 4 where the base station 102 receives thenext uplink from a CPE 104.

Returning to decision block 608, if additional air link resources arenot available, flow moves to a block 610 where the precedence module 210suspends existing connections between the base station 102 and the CPEs104. As described above, the precedence module 210 can, for example,suspend connections only between the base station and the affected CPE,randomly suspend connections between the base station and all of theCPEs in a sector 106, or suspend connections between the base stationand all of the CPEs in the sector in a round-robin fashion. Further, theprecedence module 210 can randomly suspend connections between the basestation and the CPEs that have a lower precedence priority than otherconnections. Alternatively, the precedence module 210 can suspend theconnections that have a lower precedence priority in a round-robinfashion. The process moves to block 606 as described above where themore robust PHY mode is applied for the existing connection. The processthen returns to block 402 of FIG. 4 where the base station 102 receivesthe next uplink from a CPE 104.

FIG. 6 is a flowchart illustrating the process of call admission controlfor a new connection between a CPE and the base station. This processcan be implemented at a base station. Alternatively, this process isperformed at the CPE. Flow begins in start block 500. Flow proceeds toblock 502 where the base station receiver module receives a request fora new connection. The process continues to block 504 where the CACmodule 206 sums the hard bandwidth commitments between the CPEs and basestation based on the planned modulations of the CPEs. Next, at a block506, the control module 212 determines an air link line rate for theexisting connections between the base station and CPEs based on thereference PHY mode. Flow moves to a decision block 508 where the (ACmodule 206 determines whether the air link line rate determined at block506 exceeds the hard bandwidth commitments determined at block 504. Ifthe air link line rate exceeds the hard bandwidth commitments, theprocess continues to a block 510 where the CAC module 206 allows the newconnection. However, air link resources are not initially allocated tothe connection since the connection has been allowed based on theplanned PHY modes of the CPEs and base station. The CPEs and basestation could be operated at a more robust PHY mode than their plannedPHY mode.

Flow proceeds to block 512 where the control module 212 determines thehard bandwidth commitments for the existing connections between the basestation 102 and CPEs 104 based on the current PHY mode for eachconnection. Flow moves to a decision block 514 where the precedencemodule 210 determines whether the air link line rate determined at block506 exceeds the hard bandwidth commitments between the CPEs and basestation determined at block 512. If the air link line rate exceeds thehard bandwidth commitments, the process continues to a block 516 wherethe base station allocates air link resources to the new connection.Flow then returns to block 502 where the base station 102 receives arequest for a new connection.

Returning to decision block 514, if the air link line rate does notexceed the hard bandwidth commitments, flow proceeds to a decision block518 where the precedence module 210 determines whether additional airlink resources are available. These additional air link resources caninclude available bandwidth in the uplink subframe 302 and availablebandwidth in the downlink subframe 304 (see FIG. 2). If additional airlink resources are available, flow proceeds to block 516 where the basestation allocates air link resources to the new connection. Flow thenreturns to block 502 where the base station 102 receives a request for anew connection.

Returning to decision block 518, if additional air link resources arenot available, flow moves to a block 520 where the precedence module 210suspends existing connections between the base station 102 and the CPEs104. As described above, the precedence module 210 can, for example,suspend connections only between the base station and the affected CPE,randomly suspend connections between the base station and all of theCPEs in a sector 106, or suspend connections between the base stationand all of the CPEs in the sector in a round-robin fashion.Alternatively, the new connection is accepted into a suspended statesince the precedence module 210 has already determined which of theother connections are to be suspended. Further, the precedence module210 can randomly suspend connections between the base station and theCPEs that have a lower precedence priority than other connections.Alternatively, the precedence module 210 can suspend the connectionsthat have a lower precedence priority in a round-robin fashion. Theprocess moves to block 516 where the base station allocates air linkresources to the new connection. Flow then returns to block 502 wherethe base station 102 awaits a request for a new connection.

Returning to decision block 508, if the air link line rate does notexceed the hard bandwidth commitments, flow proceeds to a block 522where the CAC module 206 denies the new connection. The process thenreturns to block 502 to await the next request for a new connection.

The foregoing description details certain embodiments of the invention.It will be appreciated, however, that no matter how detailed theforegoing appears in text, the invention can be practiced in many ways.As is also stated above, it should be noted that the use of particularterminology when describing certain features or aspects of theembodiments should not be taken to imply that the terminology is beingre-defined herein to be restricted to including any specificcharacteristics of the features or aspects of the embodiment with whichthat terminology is associated. The scope of the embodiments shouldtherefore be construed in accordance with the appended claims and anyequivalents thereof.

1. A method for allocating bandwidth among connections in a wirelesscommunication system between a base station and associated customerpremise equipments (CPEs), including a requesting CPE, where themodulation scheme of the uplinks and downlinks can be varied over time,the method comprising: receiving a request for additional bandwidth foran existing connection from a requesting CPE; summing hard bandwidthcommitments of a base station and CPEs associated with the base stationbased on a planned modulation scheme for each connection; determining anair link line rate between the base station and associated CPEs; andallocating additional bandwidth to the requesting CPE if the air linkline rate exceeds the hard bandwidth commitments and determining asecond hard bandwidth commitment for the existing connections betweenthe base station and the associated CPEs based on a current modulationscheme for each connection where the current modulation scheme for atleast one of the connections is different than the planned modulationscheme for that connection, else denying the bandwidth request; if theair link line rate exceeds the second hard bandwidth commitments,allocating air link resources to the requesting CPE, else denying therequest for additional bandwidth.
 2. The method of claim 1, furthercomprising de-allocating bandwidth from existing connections to decreasethe hard bandwidth commitments.
 3. The method of claim 2, whereinde-allocating bandwidth comprises changing the modulation scheme of oneor more of the CPEs.
 4. The method of claim 2, wherein de-allocatingbandwidth comprises changing the modulation scheme of the base station.5. The method of claim 2, wherein de-allocating bandwidth compriseschanging the modulation scheme to a less robust modulation scheme. 6.The method of claim 2, wherein de-allocating bandwidth compriseschanging a forward error correction scheme.
 7. The method of claim 2,wherein de-allocating bandwidth from existing connections is based on apriority of an existing connection.
 8. The method of claim 1, whereinthe additional air link resources include available bandwidth in anuplink subframe and available bandwidth in a downlink subframe.
 9. Themethod of claim 1, wherein the hard bandwidth commitments are summedwith reference to the modulation scheme used to determine the air linkrate.
 10. The method of claim 1, wherein summing the hard bandwidthcommitments between the base station and associated CPEs is based on aplanned modulation scheme and a forward error correction scheme for eachconnection.
 11. The method of claim 1, further comprising: assigning apriority value to each of the existing connections; and suspending atleast one of the existing connections based on the assigned priorityvalue.
 12. The method of claim 1, wherein summing the hard bandwidthcommitments for the existing connections between the base station andthe associated CPEs is further based on a forward error correctionscheme for each connection.
 13. The method of claim 1, wherein the hardbandwidth commitments include a minimum cell rate (MCR) portion of aguaranteed frame rate (GFR) connection.
 14. The method of claim 1,wherein the hard bandwidth commitments include some function ofsustainable cell rate (SCR) for variable bit rate (VBR) and variable bitrate real-time (VBR-rt) connections.
 15. The method of claim 1, whereinthe hard bandwidth commitments include measured bandwidth requirementsfor connections to provide a quality of service.
 16. A method forallocating bandwidth among connections between a base station andassociated customer premise equipment (CPE) in a wireless communicationsystem that supports adaptive modulation schemes, the method comprising:receiving a request for additional bandwidth for an existing connectionfrom a requesting CPE; summing hard bandwidth commitments of the basestation and CPEs associated with the base station based on a plannedmodulation scheme for each connection; determining an air link line ratewhich represents the amount of bandwidth available between the basestation and associated CPEs; and allocating additional bandwidth to therequesting CPE if the air link line rate exceeds the hard bandwidthcommitments, else determining if a second CPE has a lower priority thanthe requesting CPE and if it does, de-allocating bandwidth from thesecond CPE and allocating additional bandwidth to the requesting CPE.17. A method for controlling connections between a base station andassociated customer premise equipment (CPE) in a wireless communicationsystem where the modulation scheme of the uplink and downlink can changeover time, the method comprising: receiving a request for additionalbandwidth from a requesting CPE; determining selected modulation schemesfor the plurality of CPEs based on their planned modulation techniquesand quality of service requirements; determining a reference line ratefor the communication system when using a reference modulation scheme;determining multiplicative rates for normalizing CPEs selectedmodulation schemes to the reference modulation scheme; comparing thereference line rate to bandwidth requirements using the normalizedselected modulation schemes; allowing or denying the request foradditional bandwidth based on the comparison.
 18. A method forallocating bandwidth among connections in a wireless communicationsystem between a base station and associated customer premise equipments(CPEs), including a requesting CPE, where the modulation scheme of theuplinks and downlinks can be varied over time, the method comprising:receiving a request for additional bandwidth for an existing connectionfrom a requesting CPE; summing bandwidth commitments of the base stationbased on current modulation schemes for each connection, where thecurrent modulation scheme for at least one of the connections isdifferent from a planned modulation scheme for that connection;determining an amount of available bandwidth of the base station; andallocating additional bandwidth to the requesting CPE if the availablebandwidth exceeds the bandwidth commitments, else determining if asecond CPE has a lower preference than the requesting CPE and if itdoes, de-allocating bandwidth from the second CPE and allocatingadditional bandwidth to the requesting CPE.
 19. A base station in awireless communication system where the modulation scheme of the uplinksand downlinks can be varied over time, the base station comprising: areceive module that receives a request for additional bandwidth from arequesting customer premise equipment (CPE); and a control module thatsums hard bandwidth commitments of the base station and CPEs associatedwith the base station based on a planned modulation scheme for eachconnection, determines an air link line rate between the base stationand associated CPEs, allocates additional bandwidth to the requestingCPE if the air link line rate exceeds the hard bandwidth commitments anddetermines a second hard bandwidth commitment for the existingconnections between the base station and the associated CPEs based on acurrent modulation scheme for each connection where the currentmodulation scheme for at least one of the connections is different thanthe planned modulation scheme for that connection, else denying the newconnection, and if the air link line rate exceeds the second hardbandwidth commitments, allocates air link resources to the requestingCPE, else denying the request for additional bandwidth.
 20. Acommunication system that allocates bandwidth among existing connectionsbetween a base station and a plurality of customer premise equipments(CPEs) the system comprising: a first CPE having a first modem thatmodulates data using a first current modulation scheme and a firstinitial modulation scheme different from the first current modulationscheme; a second CPE having a second modem that modulates data using asecond current modulation scheme and a second initial modulation scheme;a base station having a third modem that transmits and receives data toand from the first and second CPEs; and a control module that determineswhether to re-allocate bandwidth among the first and second CPEs inresponse to bandwidth requests from the CPEs, by summing bandwidthcommitments of the base station based on first current modulation schemeand the second current modulation scheme, determining an amount ofavailable bandwidth of the base station, and if the available bandwidthexceeds the bandwidth commitments, allocates additional bandwidth to theCPE requesting additional bandwidth, else determining if a second CPEhas a lower preference than the requesting CPE and if it does,de-allocating bandwidth from the second CPE and allocating additionalbandwidth to the requesting CPE.
 21. The system of claim 20, wherein thecontrol module is located at the first CPE.
 22. The system of claim 20,wherein the control module is located at the base station.
 23. Thesystem of claim 20, wherein the third modem comprises: a transmittermodule configured to convert digital data to a modulated analog signal;and a receiver module configured to demodulate an analog modulatedsignal to digital form.
 24. The system of claim 23, wherein the thirdmodem further comprises: a Receive Signal Quality (RSQ) module coupledwith the receiver module and configured to monitor signal quality ofexisting connections between the first CPE and the base station, and thesecond CPE and the base station; and a control module interfaced withthe RSQ module and the transmitter module, and configured to select thefirst current modulation scheme for the first CPE based on the signalquality monitored by the RSQ module, and configured to select the secondcurrent modulation scheme for the second CPE based on the signal qualitymonitored by the RSQ module.
 25. The system of claim 24, wherein thethird modem further comprises a precedence module, interfaced with thecontrol module, that identifies priorities associated with the CPEs andbandwidth is allocated among the CPEs based in part on their associatedpriorities.
 26. A method for allocating bandwidth among connectionsbetween a base station and a plurality of customer premise equipment(CPEs) in a wireless communication system wherein the base station andthe plurality of CPEs each are configured to adaptively adjust channelcharacteristics for an uplink which includes one or more connections,wherein a planned modulation scheme is selected for the uplink andwherein a current modulation scheme corresponds to the modulationtechnique used by a first CPE to transmit data to the base station, themethod comprising: receiving an uplink that is modulated by the firstCPE using a first modulation scheme; determining a quality for a channelparameter for the uplink; comparing the quality with a first modulationscheme threshold value; determining if the quality is less than thefirst modulation scheme threshold value, and if it is then determiningif additional bandwidth is available to allocate to the CPE bydetermining a normalized hard bandwidth requirement and comparing it toan air link line rate, wherein if additional bandwidth is available thenallocating it to the CPE, else replacing the first modulation schemethreshold value with a second modulation scheme threshold value.
 27. Themethod of claim 26, wherein the second modulation scheme threshold valueis less than the first modulation scheme threshold value.
 28. A computerprogram product, comprising: computer-readable medium comprisingcomputer instructions that when executed cause a computer to: receivinga request for additional bandwidth for an existing connection from arequesting CPE, summing hard bandwidth commitments of the base stationand CPEs associated with the base station based on a planned modulationscheme for each connection; determining an air link line rate whichrepresents the amount of bandwidth available between the base stationand associated CPEs; and allocating additional bandwidth to therequesting CPE if the air link line rate exceeds the hard bandwidthcommitments, else determining if a second CPE has a lower priority thanthe requesting CPE and if it does, de-allocating bandwidth from thesecond CPE and allocating additional bandwidth to the requesting CPE.29. A computer program product, comprising: computer-readable mediumcomprising computer instructions that when executed cause a computer to:receiving a request for additional bandwidth for an existing connectionfrom a requesting CPE; summing hard bandwidth commitments of a basestation and CPEs associated with the base station based on a plannedmodulation scheme for each connection; determining an air link line ratebetween the base station and associated CPEs; and allocating additionalbandwidth to the requesting CPE if the air link line rate exceeds thehard bandwidth commitments and determining a second hard bandwidthcommitment for the existing connections between the base station and theassociated CPEs based on a current modulation scheme for each connectionwhere the current modulation scheme for at least one of the connectionsis different than the planned modulation scheme for that connection,else denying the bandwidth request; if the air link line rate exceedsthe second hard bandwidth commitments, allocating air link resources tothe requesting CPE, else denying the request for additional bandwidth.